Hepatitis C virus (HCV) is a major global health problem, with an estimated 150-200 million people infected worldwide, including at least 5 million infected individuals within the European Union (Pawlotsky, 2004). According to the World Health Organization, 3 to 4 million new infections occur each year. The infection is often asymptomatic. However, the majority of HCV-infected individuals develop chronic infection (Hoofnagle, 2002; Lauer, 2001; and Seeff, 1995). Chronic HCV infection frequently results in serious liver disease, including fibrosis and steatosis (Chisari, 2005). About 20% of patients with chronic HCV infection develop liver cirrhosis, which progresses to hepatocellular carcinoma in 5% of the cases (Hoofnagle, 2002).
Chronic HCV infection is the leading indication for liver transplantations (Seeff, 2002). Unfortunately, liver transplantation is not a cure for hepatitis C; viral recurrence is an invariable problem and leading cause of graft loss (Brown, 2005). No vaccine protecting against HCV is available. Current therapies include administration of ribavirin and/or interferon-alpha (IFN-α), two non-specific anti-viral agents. Using a combination treatment of pegylated IFN-α and ribavirin, persistent clearance is achieved in about 50% to 80% of patients with chronic hepatitis C. However, a large number of patients have contraindications to one of the components of the combination, cannot tolerate the treatment, do not respond to IFN therapy at all or experience a relapse when administration is stopped. In addition to limited efficacy and substantial side effects such as neutropenia, haemolytic anemia and severe depression, current antiviral therapies are also characterized by high cost.
Until recently, the development of more effective therapeutics to combat HCV infection has been hampered by the lack of a cell culture system supporting HCV replication. Robust production of infectious HCV in cell culture has now been achieved using a unique HCV genome derived from the blood of a Japanese patient with fulminant hepatitis C (JFH-1) (Wakita, 2005; Lindenbach, 2005; Zhong, 2005). The ability of the JFH-1 strain of HCV to release infectious particles in cell culture (HCVcc) and the development of retroviral HCV pseudoparticles (HCVpp) (Bartosch, 2003; Hsu, 2003) have allowed the complete viral life cycle to be explored. This, in turn, has led to the development of new antiviral agents targeting HCV protein processing and replication. However, many of these agents have proved to be toxic and highly susceptible to the development of viral resistance, suggesting that a different strategy is needed for the treatment of HCV infection.
HCV is a positive strand RNA virus classified in the Hepacivirus genus, within the Flaviviridae family. Translation of the major open reading frame of the HCV genome results in the production of an approximately 3000 amino acid long polyprotein, which is cleaved co- and post-translationally by the coordinated action of cellular and viral proteases into at least 10 mature proteins, including two envelope glycoproteins (E1 and E2). HCV initiates infection by attaching to molecules or receptors on the surface of hepatocytes. Since HCV entry is the first step of virus-host interactions, it represents a promising target for antiviral therapies. Several cell surface molecules have been identified that interact with HCV during viral binding and entry. These include the tetraspanin CD81 (Pileri, 1998), the scavenger receptor class B type I (SB-RI) (BScarselli, 2002), the tight junction proteins Claudin-1 (CLDN1) (Evans, 2007) and Occludin (Ploss, 2009), highly sulphated heparin sulphate (Barth, 2003), and the low-density lipoprotein (LDL) receptor (for review, see Barth, 2006 and Zeisel, 2008). All of these factors are expressed in many tissues and are not liver-specific. Although over-expression of CD81, SR-BI and tight junction proteins can confer HCV susceptibility to certain cell lines, other cell lines expressing the identified entry factors remain non-permissive. These findings suggest the presence of other co-entry factors mediating or modulating HCV entry.
Viruses are known to utilize signalling pathways of their target cells to their advantage during one or more steps of their life cycling including entry, internalization, replication and release (Cirone, 1990; Constantinescu, 1991; Pelkmans, 2005; Root, 2000; and Sieckarski, 2003). In recent years, it has become clear that the formation exchange between incoming viruses and the host cell during the first steps of virus-host interaction is not limited to the cues given to the virus by the cell resulting in cellular binding and entry of the virus. For many viruses, virus-host interaction resembles a two-way dialogue in which the virus takes advantage of the cell's own signal transduction systems to transmit signals to the cells (Smith, 2004). These signals—usually generated at the cell surface—induce changes that facilitate entry, prepare the cells for invasion and neutralize host defenses. Using a genomic analysis of responses to HCV envelop glycoproteins binding to hepatoma cells, the laboratory of the Applicants had previously demonstrated that binding of HCV envelop glycoproteins to host cells results in a cascade of intracellular signals modulating cellular gene expression, which may condition the cell for support of viral propagation (Fang, 2006).